Christopher is 3 times as old as Kevin and is also 8 years older than Kevin. How old is Kevin?
Solution: We can use the given information to write down two equations that describe the ages of Christopher and Kevin. Let Christopher's current age be $c$ and Kevin's current age be $k$ $c = 3k$ $c = k + 8$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $k$ , and both of our equations have $c$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $3k$ $-$ $ (k + 8)$ which combines the information about $k$ from both of our original equations. Solving for $k$ , we get: $2 k = 8$ $k = 4$.